The influence of nucleotide sequences at and near ribosome-binding site on translational efficiency of the Bacillus subtilis rho gene

The Bacillus subtilis rho gene encodes the transcription termination factor Rho that is produced at a low level in B. subtilis cells. No typical Shine-Dalgarno (SD) sequence lies at an appropriate distance from the translational start site of rho. However, the nucleotide sequence GTGGTG present upstream of the rho translational start site is highly conserved among rho genes of Bacilli. Base substitutions at the central GG or its downstream T abolished expression of rho-lacZ translational fusion, suggesting their importance in rho expression. Mutations at the relatively conserved sequence AAAG located further upstream of GTGGTG could also affect translational efficiency. Moreover, insertion of two or three nucleotides between these two conserved regions abrogated rho-lacZ expression, suggesting that the spacing is important. The possibility that the rho gene may contain a split SD sequence is discussed.